Using PowerTap test to decide a new frame?

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This analysis concluded frame flex may reduce the peak power within a pedal stroke, but generally has no significant effect on average power over a full pedal stroke:
http://www.bikethink.com/Frameflex.htm

It will be interesting if you observe a difference.

Dan

This analysis concluded frame flex may reduce the peak power within a pedal stroke, but generally has no significant effect on average power over a full pedal stroke:
http://www.bikethink.com/Frameflex.htm

It will be interesting if you observe a difference.

Dan

Very cool link. I guess I was way off base. If one were to assume that all of the energy was lost in his model, that would be 6.5 whole watts in a 1300w sprint! :rolleyes:

So do you really think that the frame is sucking up 80w? (seriously)

Sigh....

"Could be coincidence, random varience, losses in frame. Who knows."

Is there something wrong with my gedanken experiment?


I wouldn't dare consider your gedanken and how you experiment with it.

Very cool link. I guess I was way off base. If one were to assume that all of the energy was lost in his model, that would be 6.5 whole watts in a 1300w sprint! :rolleyes:In particular, the plot on:
http://www.bikethink.com/Power_output.htm

shows no power loss evident to the resolution of the plot. So as you said, even 6.5 W/1300 W is an upper bound estimate.

That said, good sprinters seem to like stiff bottom brackets, not that a whippy Vitus Alumninum frame seemed to slow Sean Kelly, much....

Dan

Doing sprints in training, I've never come closer than 80 (peak) watts on the steel bike to what I do on the carbon bike. Could be coincidence, random varience, losses in frame. Who knows. But the numbers are consistantly higher by about 80 to 100 watts on the carbon bike.

How do the max 5s numbers compare?

Some places to check:
http://weightweenies.starbike.com/phpBB2/viewtopic.php?t=25692&highlight=tour+tests
and
http://fairwheelbikes.com/forum/viewtopic.php?t=2617

Thanks a mil!
Dave

If you're looking at a 3-4k frame I seriously don't think that you should be that worried about frame flex.

If it's strong enough for the like of McEwen / Boonen........

If you're looking at a 3-4k frame I seriously don't think that you should be that worried about frame flex.Even if formulas and experiments don't show a significant difference in efficiency of a "stiff" frame, there's nothing wrong with wanting a frame with that ride quality. There's something to be said for a bike that feels stiff and seems to rocket forward when you stand up and sprint...even if it's just a subjective observation.

You may even gain a small benefit from the placebo effect...if you think your frame is more efficient, you may go faster! ;)

Even if formulas and experiments don't show a significant difference in efficiency of a "stiff" frame, there's nothing wrong with wanting a frame with that ride quality. There's something to be said for a bike that feels stiff and seems to rocket forward when you stand up and sprint...even if it's just a subjective observation.

You may even gain a small benefit from the placebo effect...if you think your frame is more efficient, you may go faster! ;)Right -- feel can be important, I agree. I was commenting on the experiment to measure a tangible, quantitative effect.

There's been a big fuss made, for example, about crank length, with Lennard Zinn having published results showing it has little effect on power production. To me, this is another issue of the value of comfort -- I don't care if I am able to produce the same power, unless I can do so at least as comfortably. I doubt a rock in my shoe would much reduce my power production, either.

So I think frame stiffness is a matter of "feel" more than a fundamental biomechanical efficiency matter. But feel is still real.

So much food for thought I think my brain has added a few pounds!

Now I need a lighter flexier frame just to make up the difference :p